Hydropneumatic accumulators for motor vehicles are primarily geared toward air spring applications in half band, full band and level control suspension systems. An air spring can be used as an energy storage device, pulsation dampener, or shock transient absorption device in such systems.
Recently, a demand has developed for accumulators for active vehicle suspension systems which provide vehicle handling control safety; and, improve comfort and vehicle handling. Comfort and handling are improved by providing a level ride on irregular road surfaces and during braking, cornering, speed changes and lane changes. Active suspensions are also effective in countering the aerodynamic forces of winds and large highway trucks.
Vehicle attitude changes are undesirable because they produce wheel caster and chamber changes which cause undesirable steering effects and increase tire wear. Active suspensions are beneficial for passenger vehicles, trucks, construction equipment, as well as military vehicles, such as army personnel carriers which often operate on irregular terrain.
Heretofore, suspension accumulators have incorporated closed mouth bladders made of natural and synthetic rubber materials, such as Nitrile, Butyl, Viton and Neoprene. One problem with current accumulators is that bladders develop leaks during severe and extended service.
Bladder leaks can occur from fatigue or from bladder contact with a port assembly. Leaks adversely affect vehicle ride handling and safety and increase the cost of vehicle ownership. Leaks are also undesirable because they adversely affect the reputation of an automobile's manufacturer.
Polyurethane materials are higher in strength than the aforedescribed synthetic rubber materials. Moureaux, U.S. Pat. No. 5,036,110 discloses a bladder for a hydropneumatic accumulator having a laminated bladder made from laminating layers of polyurethane to opposite sides of a layer formed by the reaction of polyurethane with a copolymer of ethylene and vinyl alcohol.
Laminated bladders are undesirable because of high costs, low production rates, quality control problems and failures due to layer separation.